MPI_CART_SUB(comm, remain_dims, newcomm) | |

IN comm | communicator with Cartesian structure (handle) |

IN remain_dims | the i-th entry of remain_dims specifies whether the i-th dimension is kept in the subgrid ( true) or is dropped ( false) (logical vector) |

OUT newcomm | communicator containing the subgrid that includes the calling process (handle) |

` int MPI_Cart_sub(MPI_Comm comm, int *remain_dims, MPI_Comm *newcomm) `

` MPI_CART_SUB(COMM, REMAIN_DIMS, NEWCOMM, IERROR) INTEGER COMM, NEWCOMM, IERROR LOGICAL REMAIN_DIMS(*) `

MPI_CART_SUB can be used to partition the communicator group into subgroups that form lower-dimensional Cartesian subgrids, and to build for each subgroup a communicator with the associated subgrid Cartesian topology. If all entries in remain_dims are false or comm is already associated with a zero-dimensional Cartesian topology then newcomm is associated with a zero-dimensional Cartesian topology. (This function is closely related to MPI_COMM_SPLIT.)

** Example**

Assume that MPI_CART_CREATE(..., comm) has defined a
*(2 × 3 × 4)* grid. Let ` remain_dims = (true, false, true)`.
Then a call to,

will create three communicators each with eight processes in aMPI_CART_SUB(comm, remain_dims, comm_new),

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